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Title: Structure–Conductivity Relationships in Ordered and Disordered Salt-Doped Diblock Copolymer/Homopolymer Blends

Abstract

We examine the relationship between structure and ionic conductivity in salt-containing ternary polymer blends that exhibit various microstructured morphologies, including lamellae, a hexagonal phase, and a bicontinuous microemulsion, as well as the disordered phase. These blends consist of polystyrene (PS, M n ≈ 600 g/mol) and poly(ethylene oxide) (PEO, M n ≈ 400 g/mol) homopolymers, a nearly symmetric PS–PEO block copolymer (M n ≈ 4700 g/mol), and lithium bis(trifluoromethane)sulfonamide (LiTFSI). These pseudoternary blends exhibit phase behavior that parallels that of well-studied ternary polymer blends consisting of A and B homopolymers compatibilized by an AB diblock copolymer. The utility of this framework is that all blends have nominally the same number of ethylene oxide, styrene, Li +, and TFSI– units, yet can exhibit a variety of microstructures depending on the relative ratio of the homopolymers to the block copolymer. For the systems studied, the ratio r = [Li +]/[EO] is maintained at 0.06, and the volume fraction of PS homopolymer is kept equal to that of PEO homopolymer plus salt. The total volume fraction of homopolymer is varied from 0 to 0.70. When heated through the order–disorder transition, all blends exhibit an abrupt increase in conductivity. However, analysis of small-angle X-raymore » scattering data indicates significant structure even in the disordered state for several blend compositions. By comparing the nature and structure of the disordered states with their corresponding ordered states, we find that this increase in conductivity through the order–disorder transition is most likely due to the elimination of grain boundaries. In either disordered or ordered states, the conductivity decreases as the total amount of homopolymer is increased, an unanticipated observation. This trend with increasing homopolymer loading is hypothesized to result from an increased density of “dead ends” in the conducting channel due to poor continuity across grain boundaries in the ordered state and the formation of concave interfaces in the disordered state. The results demonstrate that disordered, microphase-separated morphologies provide better transport properties than compositionally equivalent polycrystalline systems with long-range order, an important criterion when optimizing the design of polymer electrolytes.« less

Authors:
 [1];  [2];  [2];  [1];  [1];  [3]
  1. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science
  2. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemistry
  3. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science; Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemistry
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE; National Science Foundation (NSF)
OSTI Identifier:
1330863
Resource Type:
Journal Article
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 49; Journal Issue: 18; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE

Citation Formats

Irwin, Matthew T., Hickey, Robert J., Xie, Shuyi, So, Soonyong, Bates, Frank S., and Lodge, Timothy P. Structure–Conductivity Relationships in Ordered and Disordered Salt-Doped Diblock Copolymer/Homopolymer Blends. United States: N. p., 2016. Web. doi:10.1021/acs.macromol.6b01553.
Irwin, Matthew T., Hickey, Robert J., Xie, Shuyi, So, Soonyong, Bates, Frank S., & Lodge, Timothy P. Structure–Conductivity Relationships in Ordered and Disordered Salt-Doped Diblock Copolymer/Homopolymer Blends. United States. https://doi.org/10.1021/acs.macromol.6b01553
Irwin, Matthew T., Hickey, Robert J., Xie, Shuyi, So, Soonyong, Bates, Frank S., and Lodge, Timothy P. Mon . "Structure–Conductivity Relationships in Ordered and Disordered Salt-Doped Diblock Copolymer/Homopolymer Blends". United States. https://doi.org/10.1021/acs.macromol.6b01553.
@article{osti_1330863,
title = {Structure–Conductivity Relationships in Ordered and Disordered Salt-Doped Diblock Copolymer/Homopolymer Blends},
author = {Irwin, Matthew T. and Hickey, Robert J. and Xie, Shuyi and So, Soonyong and Bates, Frank S. and Lodge, Timothy P.},
abstractNote = {We examine the relationship between structure and ionic conductivity in salt-containing ternary polymer blends that exhibit various microstructured morphologies, including lamellae, a hexagonal phase, and a bicontinuous microemulsion, as well as the disordered phase. These blends consist of polystyrene (PS, Mn ≈ 600 g/mol) and poly(ethylene oxide) (PEO, Mn ≈ 400 g/mol) homopolymers, a nearly symmetric PS–PEO block copolymer (Mn ≈ 4700 g/mol), and lithium bis(trifluoromethane)sulfonamide (LiTFSI). These pseudoternary blends exhibit phase behavior that parallels that of well-studied ternary polymer blends consisting of A and B homopolymers compatibilized by an AB diblock copolymer. The utility of this framework is that all blends have nominally the same number of ethylene oxide, styrene, Li+, and TFSI– units, yet can exhibit a variety of microstructures depending on the relative ratio of the homopolymers to the block copolymer. For the systems studied, the ratio r = [Li+]/[EO] is maintained at 0.06, and the volume fraction of PS homopolymer is kept equal to that of PEO homopolymer plus salt. The total volume fraction of homopolymer is varied from 0 to 0.70. When heated through the order–disorder transition, all blends exhibit an abrupt increase in conductivity. However, analysis of small-angle X-ray scattering data indicates significant structure even in the disordered state for several blend compositions. By comparing the nature and structure of the disordered states with their corresponding ordered states, we find that this increase in conductivity through the order–disorder transition is most likely due to the elimination of grain boundaries. In either disordered or ordered states, the conductivity decreases as the total amount of homopolymer is increased, an unanticipated observation. This trend with increasing homopolymer loading is hypothesized to result from an increased density of “dead ends” in the conducting channel due to poor continuity across grain boundaries in the ordered state and the formation of concave interfaces in the disordered state. The results demonstrate that disordered, microphase-separated morphologies provide better transport properties than compositionally equivalent polycrystalline systems with long-range order, an important criterion when optimizing the design of polymer electrolytes.},
doi = {10.1021/acs.macromol.6b01553},
url = {https://www.osti.gov/biblio/1330863}, journal = {Macromolecules},
issn = {0024-9297},
number = 18,
volume = 49,
place = {United States},
year = {2016},
month = {11}
}